CONSTRUCTION OF MULTISPECIES ALLOMETRIC

Tb Mayaka,R Eba’A-Atyi,St Momo

doi:10.26525/jtfs2017.29.3.282296

Abstract

To avoid the problem of destructive tree sampling, we tested an indirect estimation procedure whereby aboveground tree volumes are estimated using affine-transforms of traditional bole volume equations. The study compared the predictive performance of the (1) proposed procedure, (2) allometric aboveground volume equations, and (3) simple upscaling of empirical tree bole volumes (serving as benchmark procedure). The study assessed speciesand tree-individual random deviations from mean procedure effect on prediction errors. Six volume equations were each fitted to aboveground volume (a- version) and bole volume (b- version); predictions of latter volumes were affine-transformed to estimate aboveground tree volumes. Bole height, total height and diameter at breast height (dbh) were measured for 59 trees from 10 species in eastern Cameroon. The Schumacher and Hall equation ranked first in quality-of-fit. The direct and indirect approaches applied with this volume equation predicted the aboveground tree volumes equally well across all species (groupings), with bias (± RMSE of 0.153 ± 2.512 and 0.178 ± 2.56 m3 respectively. Finally, trees within species accounted for 49.3% of the total variability in volume prediction error vs only 3.5% for species. Recommendations have been made for improvement relatively to data requirements and model building.

Highlights

Tropical rainforests are the world’s most important carbon sink for mitigating the impact of carbon emission on global climate change (Houghton et al 2009, Marshall et al 2012)
Extrapolation is defined as a simple procedure whereby an independent tree measurement (D*, H*) together with a previously fitted volume equation are used to predict the tree bole volume which is mapped onto tree aboveground volume a using a scaling function, as illustrated in the bottom part of Figure 1
This study proposed an indirect approach for extrapolating aboveground tree volume using affine transformation of bole volume predictions, in an attempt to avoid the destructive sampling of trees when building multispecies allometric equations

Summary

Introduction

Tropical rainforests are the world’s most important carbon sink for mitigating the impact of carbon emission on global climate change (Houghton et al 2009, Marshall et al 2012) These forests are the main focus of the international policy to ‘reduce emissions from deforestation and degradation’ in developing countries (REDD+) (Kuyah et al 2012, Marshall et al 2012, Angelsen et al 2013) under which forest carbon stocks must be estimated with as much accuracy and precision as possible. These include (1) high plant diversity, often exceeding 300 different species ha-1 (Lewis et al 2004), (2) high variability in forest types, wood densities, tree heights, biomass and volume (Feldpausch et al 2011, Lewis et al 2013), (3) poor knowledge of natural stand dynamics such as growth, mortality and recruitment (Picard et al 2012b, Mayaka et al 2014) and (4) human disturbances (logging and deforestation) responsible for releasing greenhouse effect gas (IPCC 2007, Marshall et al 2012)

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